Backup file bigger than original: Am i getting a perfect 1:1 copy?




So far this forum have been answering all my doubts to a point that i didn’t need to post any new thread. But now i searched and still didn’t found the answer to my somewhat technical question.
I backup some of my DVD’s with CloneDVD and were surprised to find that the total size of the backup file was a little bigger than the original: sectors, size, time and last physical sector of data area as it was shown on ImgBurn. I checked with DVDShrink and saw that the movie, menus, extras, languages and subtitles had the same size in MB as the original, so apparently no problems there.
I was wondering from where that extra size comes. It’s not very much and – what’s even stranger – differs from DVD to DVD: with Crash i got an extra 144 sectors, 294912 plus in size and 2:00 in time and with double indemnity i got 192 extra sectors, 393216 plus in size and 2:42 in time.
I know that CloneDVD alters the “Source Media Application Identifier (to ELBY CLONEDVD) and Source Media Implementation Identifier (to ELABORATE BYTES) and was wondering if that as something to do with it.
When i use ImgBurn, unlike CloneDVD, i get a file that as the exact same size as the original.
In spite of the data (movie, extras…) seems to occupy the same space in the backup i’m a little afraid that i’m not getting an exact copy of the original, wich my objective.

Important note: The backups in CloneDVD were made on SL media because it was enough for the 1:1 copy of the original DVD. For DL i always use ImgBurn.

Thanks everyone